a) A research engineer for a tire manufacturer is investigating tire life for a
ID: 3061200 • Letter: A
Question
a) A research engineer for a tire manufacturer is investigating tire life for a new rubber compound and has built 36 tires and tested them to end-of-life in a road test. The sample mean and standard deviation are 64.9 and 2.3 thousand kilometers. Find a 99% upper bound for the mean life in road test. (round the answer to three digits)
b) A research engineer for a tire manufacturer is investigating tire life for a new rubber compound and has built 36 tires and tested them to end-of-life in a road test. The sample mean and standard deviation are 62.1 and 2 thousand kilometers. Find a 98% confidence interval for the mean life in road test. Write the interval as (A ; B) and give the value of A (round the answer to three digits)
Explanation / Answer
Ans:
a)sample size,n=36
df=36-1=35
confidence level=0.99
t value=2.438
99% upper bound=64.9+2.438*2.3/sqrt(36)
=64.9+0.935
=65.834
b)critical t value(two tailed) for 98% CI is 2.438
98% confidence interval for population mean
=62.1+/-2.438*2/sqrt(36)
=62.1+/-0.813
=(61.287, 62.913)
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